The present invention relates to a semiconductor manufacturing method and a semiconductor manufacturing apparatus for manufacturing a semiconductor integrated circuit by forming different pattern layers of semiconductor integrated circuits with different pattern exposure systems, and particularly to a semiconductor manufacturing method and a semiconductor manufacturing apparatus in which a reliability can be increased by increasing an alignment accuracy among the respective pattern exposure systems, and semiconductor devices manufactured by such semiconductor manufacturing method and semiconductor manufacturing apparatus.
Heretofore, in the semiconductor manufacturing process using a pattern exposure system (using lithography technologies), there exist a large number of working processes in which there is alignment of the patterns formed on the semiconductor wafer in the preceding process and new different patterns are formed on the previously-formed pattern. Recently, there is an increasing demand for more microminiaturization with respect to these lithography technologies. As described in "Japanese Journal of Applied Physics (J.J.A.P.)" Series 4, Proc. Of 1999 Intern. MicroProcess Conference pp. 58-63, for example, a method is described in which layers required to have high resolution are formed by an electron beam lithography system and other layers are formed by other lithography systems (exposure system) such as a stepper using i rays or an excimer laser as a light source, i.e. a mix-and-match manufacturing method. In such a mix-and-match manufacturing method, the most important factor to consider is alignment accuracy between the layer exposed by the optical exposure system and the layer lithographed by electron beams.
FIG. 2 is a diagram showing an example of a method for accomplishing alignment lithography.
In the aforementioned mix-and-match manufacturing method, an example of a method of accomplishing alignment lithography on an underlayer pattern will be described with reference to FIG. 2. As shown in FIG. 2, on a wafer 1, there is formed a layer (a plurality of chips 3, etc.) exposed by an optical projection exposure system (hereinafter simply referred to as an optical exposure system). On this layer, there are previously exposed alignment marks 2 used in lithography alignment of the next layer together with the underlayer. These marks 2 are located at four corners of the chip 3. The position on the wafer 1 is visually confirmed by detecting the positions of these four marks 2 using an electron beam scanning or optical method.
FIG. 3 is a perspective view showing an optical exposure system and FIG. 4 is a diagram showing characteristics of a pattern exposed by the optical exposure system.
In the optical exposure system, as shown in FIG. 3, there is used an aperture 4 for uniformly converging incident light of a specific shape. Light projected from the aperture 4 is irradiated through a lens 5 onto a mask 6, a projected image is generated by projecting a pattern lithographed on the mask 6, and this projected image is demagnified by a demagnification lens comprising a plurality of lenses and then developed on the wafer 1.
A field exposed on the wafer 1 becomes a distorted pattern shown in FIG. 4 by optical characteristics of the demagnification lens 7. That is, as compared with a plan shown by broken lines, the pattern exposed in actual practice becomes a distorted shape as shown by solid lines in FIG. 4.
When a semiconductor integrated circuit is manufactured, since a relative positional relationship between the exposed pattern and the underlayer becomes important, the lithography position of the next layer should be corrected in accordance with the distortion of the pattern exposed by the optical exposure system. There are available two correction methods. One correction method is to align the exposed pattern and the underlayer by lithographing the next layer into a pattern having the same distortion in accordance with the distortion of the exposed pattern (alignment lithography). The other correction the method is to correct mask 6 itself by reverse-correcting the plan in order to remove the distortion from the exposed pattern so that the underlayer and other layers are developed on the wafer 1 by the demagnification lens 7 (mask lithography).
The technology for achieving such correction is described in JP-A-62-149127, for example. According to this technology, as shown in FIGS. 5A and 5B, a mask 6 in which distortion measurement marks 8 are disposed on the whole of the exposure area at a constant pitch in a lattice fashion is transferred onto the wafer 1 by a pattern exposure system. Then, mark position data is memorized by scanning the positions of the distortion measurement marks 8a formed on this wafer 1 with electron beams, exposure distortion data is obtained from that stored data, and the exposure positions of charged beams are corrected in accordance with distortion data. That is, there is used the above-mentioned latter method.
Recently, as the minimum work dimension of integrated circuit is increasingly reduced, a required alignment accuracy becomes approximately 50 nm and becomes more severe. Therefore, how to accurately measure the distortion of the underlayer and how to accurately correct the distortion in the alignment lithography become important problems. In addition, since the shape of the positional distortion of the pattern exposed by the optical exposure system and the distortion amount are not constant, as described in "SPIE Vol. 2725", p. 417, it becomes clear that the shape of the positional distortion and the distortion amount become different due to characteristics of the exposed pattern at the nanometer level.
FIGS. 6A and 6B are diagrams used to explain features of patterns exposed by the optical exposure system. FIG. 7 is a diagram used to explain a difference between distorted states of the patterns produced by the optical exposure system.
When a pattern comprising lines and spaces (comprising a plurality of lines) shown in FIG. 6A is transferred or when an isolated pattern shown in FIG. 6B is transferred, for example, the distorted amounts of the transferred patterns become slightly different from each other depending upon the patterns. The reason for this is that light diffracted when traveling through the mask is exposed on the underlayer at different positions of the lens in the patterns with different spatial frequencies.
The distortion amount of the optical exposure system changes mainly depending upon the position of the exposure field of the optical exposure system. Specifically, the distortion obtained when the pattern shown in FIG. 6A is transferred has a distortion shown by a broken line (a) in FIG. 7, while the distortion obtained when the pattern shown in FIG. 6B is transferred has a distortion shown by a solid line (b) in FIG. 7. A difference between the two distortion amounts ranges from approximately 30 to 50 nm at maximum and a required alignment accuracy is less than approximately 50 nm so that a proper alignment cannot be made, which causes an extremely serious problem. Accordingly, even when the electron beam lithography pattern is corrected by the distortion as measured based on the conventional standard pattern, the pattern has different distortions depending upon the shape of the pattern of the underlayer so that the lithography pattern cannot be corrected appropriately.
As described above, the lens distortion amount of the optical exposure apparatus is determined by a combination of the position of the exposure field and the shape of the exposed pattern. Accordingly, when the pattern is exposed by a combination of different lithography techniques, i.e. the optical exposure system and an electron beam direct lithography system, according to the conventional method, the lithography pattern is not corrected by considering the exposure conditions and the pattern state of the underlayer, thereby making it difficult to expose the pattern by the combination of the optical exposure system and the electron beam direct lithography system at high accuracy under 50 nm.
While the above-mentioned problem has been described so far as a problem associated with high alignment accuracy in the combination of different exposure systems such as the electron beam lithography system and the optical exposure system, when a plurality of patterns are exposed together by the same optical exposure system, if the features of the pattern shapes are considerably different in the layers, then exactly the same problem will arise.